Circuitry for portable lighting devices and portable rechargeable electronic devices

ABSTRACT

A portable electronic device, such as a flashlight, with a circuit for reducing the initial surge of current that is sent through the lamp filament when a flashlight is turned on is provided. The circuit reduces the stresses placed on the lamp bulb when it is turned on, thereby extending the life expectancy of the lamp bulb. A flashlight with beacon mode that produces light according to a duty cycle of less than 11% is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of prior co-pending U.S. patent application Ser.No. 11/351,307, filed Feb. 8, 2006, which is in turn acontinuation-in-part of prior U.S. patent application Ser. No.11/007,771, now issued U.S. Pat. No. 7,579,782, filed Dec. 7, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the present invention relates to portable electronicdevices, including hand held portable lighting devices, such asflashlights, and their circuitry.

2. Background

Various hand held or portable lighting devices, including flashlightdesigns, are known in the art. Flashlights typically include one or moredry cell batteries having positive and negative electrodes. In certaindesigns, the batteries are arranged in series in a battery compartmentof a barrel or housing that can be used to hold the flashlight. Anelectrical circuit is frequently established from a battery electrodethrough conductive means which are electrically coupled with anelectrode of a lamp bulb. After passing through the lamp bulb, theelectric circuit continues through a second electrode of the lamp bulbin electrical contact with conductive means, which in turn are inelectrical contact with the other electrode of a battery. Incandescentlamp bulbs include a bulb filament. Typically, the circuit includes aswitch to open or close the circuit. Actuation of the switch to closethe electrical circuit enables current to pass through the lamp bulb andthrough the filament, in the case of an incandescent lamp bulb, therebygenerating light.

Traditional flashlights use a mechanical switch to “turn on” theflashlight. This is achieved by mechanically connecting two contacts andallowing current to flow from the positive terminal of the batteries,through the lamp, and back to the negative terminal of the batteries.One of the disadvantages of a mechanical switch is that they are proneto wear and tear as well as oxidation of the elements that physicallymake and break the circuit. Mechanical switches also do not permitautomated or regulated modes of activating and deactivating aflashlight.

Another disadvantage of traditional flashlights is that when they areswitched on they instantly allow large amounts of current to flow fromthe batteries through the lamp filament, thereby stressing the filament.This surge of current occurs because the resistance of the lamp'sfilament is very low when the filament is cold.

Essentially a lamp filament is a piece of wire that initially acts as ashort circuit. The filament resistance builds as the filament heatsuntil the point where light is emitted. Consequently, when theflashlight is initially turned on, a significantly greater amount ofcurrent than the bulb is designed to handle flows through the lamp.Although the current surge during this transient stage exceeds thebulb's design limits, the duration of the transient stage is shortenough that bulbs generally survive the current surge. Over time,however, this rush of current causes damage to the lamp by stressing thefilament and ultimately failure of the lamp filament. Indeed, it isgenerally during this transient stage that a lamp filament willultimately fail.

Yet another disadvantage of traditional flashlights is that they aregenerally powered with alkaline or dry cell batteries. Alkaline or drycell batteries, when exhausted, are discarded and users have to buy newones to replace the depleted ones. Replacing batteries is aninconvenience and an additional expense to a flashlight user.Furthermore, alkaline or dry cell batteries are heavy, thereby adding tothe overall weight of the flashlight.

Rechargeable lead-acid batteries were developed to replace alkaline anddry batteries. These types of batteries have the advantages of beingrechargeable and dischargeable for repeated use. They are, however,relatively large and must be refilled with liquid electrolyte afterbeing used for a period of time. Due to their bulky size and weight,even heavier than alkaline/dry cell batteries, rechargeable lead-acidbatteries are usually used with wall-mounted safety lighting fixtures,motorcycles, and automobiles, but are generally not considered suitablefor use with portable lighting devices, such as flashlights.

Nickel-cadmium batteries and nickel-metal hydride batteries have beenused to replace conventional batteries in flashlights. Nickel-cadmiumand nickel-metal hydride batteries have the advantages of being light inweight, convenient for use, and repeatedly rechargeable anddischargeable. However, these batteries have a disadvantage of causingheavy metal pollution. Moreover, the nickel-cadmium and nickel-metalhydride batteries have the so-called battery memory effect. Thus, inorder to avoid shortening the life of the batteries, it is necessary todischarge any unused power of these types of batteries before they canbe recharged.

An improved rechargeable energy source for portable electronic devicesis the lithium-ion battery. Lithium-ion batteries have a higher energydensity and a lower self-discharge rate than nickel-cadmium andnickel-metal hydride batteries. Lithium-ion batteries also have a higherenergy to weight ratio than nickel-cadmium and nickel-metal hydridebatteries. However, a lithium-ion battery can explode if it is chargedbeyond its safe limits, or if its terminals are shorted together.Further, over discharging a lithium-ion battery can permanently damagethe lithium-ion cell. Accordingly, most lithium-ion batteries are madeavailable in a battery pack that includes a built-in protection circuitthat has over charge, over discharge, and short circuit protectioncapabilities. This battery pack protection circuit internally blockscurrent from flowing from the lithium-ion battery pack when a short isdetected. Thus, if there is a short across the recharging contacts forthe device, the battery pack protection circuit trips and the electronicdevice will cease to operate

To avoid such inadvertent interruptions, recharging contacts of portableelectronic devices that are powered by a rechargeable lithium-ion battypack have the contacts in hard to reach or hidden locations.Unfortunately, such a configuration requires the use of plugs, specialinserts, alignment tabs or a complex cradle to recharge the batteries.Obstructing access to the recharging contacts is not, however, a viablesolution in the case of flashlights or other rechargeable devices wheredesign requirements dictate that the charging contacts or rings beexposed.

If rechargeable lithium-ion batteries were used in a flashlight withexposed charge rings and the user accidentally created a short acrossthe exposed charge contacts with a metal object such as his or her carkeys, the lamp would go off until the metal object creating the shortcircuit is removed. Such inadvertent interruptions may be dangerous whena user is working in an unlit area, especially for law enforcement andemergency response personnel. And, while a simple diode can be placed inthe recharging circuit to prevent accidental short circuits from beingcreated across the charging rings or contacts for other rechargeablebattery chemistries, such as nickel-cadmium and nickel metal hydride,this solution is not viable for lithium-ion battery packs. A simplediode cannot be used in these circumstances because the forward voltagedrop of a diode varies greatly while charging lithium-ion batteriesrequires very tight control over the termination voltage.

In view of the foregoing, rechargeable lithium-ion battery technologyhas not been adopted for use in portable electronic devices with exposedcharging contacts, such as rechargeable flashlights. A need, therefore,exists for a means of providing improved short circuit protection inrechargeable devices, such as flashlights, having exposed chargingcontacts. A separate need also exists for a flashlight with improvedcircuitry that ameliorates one or more of the problems discussed above.

SUMMARY OF THE INVENTION

It is an object of the present invention to address or at leastameliorate one or more of the problems associated with the flashlightsand/or rechargeable devices noted above.

Accordingly, in a first aspect of the invention, a portable rechargeableelectronic device, such as a flashlight, with external charging contactsand a short protection circuit is provided. The short protection circuitelectrically uncouples one of the exposed charging contacts from therechargeable power supply for the device when the charging contacts areshorted together. The charging contact is uncoupled without opening thepower circuit for the device; thus, the device can continue to operatewhile the charging contacts are shorted. The power supply for the devicemay be a rechargeable lithium-ion battery pack.

According to one embodiment, the rechargeable electronic devicecomprises a main power circuit including a DC power source and a powerconsuming load, a first charging contact electrically coupled to a firstelectrode of the power source via a first electrical path, a secondcharging contact electrically coupled to a second electrode of the powersource via a second electrical path, and a short protection circuitconfigured to open the first electrical path at a location that is notwithin the main power circuit if the first charging contact and thesecond charging contact are shorted together.

The short protection circuit preferably includes a switch interposed inthe first electrical path between the first charging contact and thefirst electrode at a location that is not within the main power circuit.The short protection circuit may be configured to open the switch if thefirst and second charging contacts are shorted together. The switch may,for example, be a transistor, including either a field effect transistoror a bipolar transistor. Preferably the switch is a p-channelmetal-oxide-semiconductor field effect transistor (MOSFET).

The short protection circuit may also include a comparing device adaptedto compare a voltage of a first input signal to a voltage of a secondinput signal and open or close the switch based on the comparison. Thevoltage of the first signal may be proportional to the voltagedifference between the first charging contact and ground and the voltageof the second signal may be proportional to the voltage of the powersource. The comparing device may, for example, comprise a comparator, anop amp, an ASIC, or a processor. When the voltage drop between the firstcharging contact and ground is approximately equal to or greater thanthe voltage of the battery, the switch is commanded to be in the “on”position by the comparing device. As a result, when the device is in itscharger energy may flow from the charging contact to the power source.When the voltage drop between the first charging contact and ground iszero, the switch is commanded to be in the “off” position. Thus, if ashort occurs between the charging contacts, the switch will be turned“off” or opened. As a result, the power source avoids any short acrossthe charging contacts and can continue to supply power to the powerconsuming load.

The rechargeable device may comprise a flashlight, and the DC powersource may comprise a rechargeable lithium-ion battery pack. In case ofa short across the charging contacts, the short protection circuit maybe configured to detect and clear the short faster than the built-inshort circuit protection of the lithium-ion battery pack. As such, theshort protection circuit ensures that the operation of the device is notinterrupted if a short occurs on the external charging contacts. This isparticularly advantageous if the rechargeable device comprises aflashlight.

In yet a further embodiment, a rechargeable flashlight is provided thatcomprises a power source, a lamp electrically coupled to the powersource through a main power circuit, a first charging contactelectrically coupled to a first electrode of the power source through afirst electrical path, a second charging contact electrically coupled toa second electrode of the power source through a second electrical path,and a logic circuit controlling a switch interposed in the firstelectrical path at a location that is not within the main power circuit.The logic circuit is configured to signal the switch to open if thefirst and second charging contacts are shorted together.

According to a second aspect of the invention, a portable lightingdevice that includes a circuit for regulating current flow through thelamp of the device is provided. The circuit preferably reduces theinitial surge of current that is sent through the lamp when the lamp isturned on. In the case of lighting devices that employ incandescent lampbulbs, such a circuit may be used to reduce the stresses placed on thelamp bulb when the lighting device is turned on, thereby extending thelife expectancy of the lamp bulb.

According to one embodiment, the lighting device comprises a main powercircuit including a power source, a light source, and an electronicpower switch, and a power control circuit. The power control circuit iselectrically coupled to the electronic power switch and adapted toregulate current flow through the electronic power switch in response toa control signal. The power control circuit may regulate the electronicpower switch when the lighting device is turned on to limit the peakcurrent that flows through the main power circuit prior to the mainpower circuit reaching a steady state. The electronic power switch maycomprise a transistor, and the light source may include a filament.Preferably the electronic power switch comprises an n-channel MOSFET andthe power control circuit applies the modified control signal to thegate of the MOSFET. The lighting device may comprise a flashlight.

In a preferred embodiment, the lighting device further comprises amicroprocessor and a mechanical switch for opening and closing anelectrical path between the power source and the microprocessor. Themicroprocessor provides the control signal to the power control circuitin response to an activation signal received from the mechanical switch,and the power control circuit modifies the control signal and appliesthe modified control signal to the electronic power switch. The voltageof the control signal may vary according to a step function when thelighting device is turned on, while the modified control signal may havea voltage that increases over time after the lighting device is turnedon. Preferably the voltage of the modified control signal increasesexponentially after the flashlight is turned on.

According to another embodiment, the lighting device comprises aflashlight having a main power circuit that includes a power source, alamp, and an electronic power switch, and a power control circuitelectrically coupled to the electronic power switch and adapted toprovide a signal to the electronic power switch while the flashlight ison. In the present embodiment, the amount of current the electronicpower switch is capable of conducting in the main power circuit isdependent on the voltage of the signal applied to the electronic powerswitch, and the power control circuit is configured to vary the voltageof the signal in a manner that increases the amount of current that canflow through the power switch over a predetermined period when theflashlight is turned on.

Preferably the predetermined period is set to be greater than the timerequired for the main power circuit to reach a steady state after theflashlight is turned on. If the lamp includes a filament, thepredetermined period is preferably greater than the thermal timeconstant of the filament. Typically, the predetermined period will be 10milliseconds or more, and more preferably the predetermined period willbe 40 milliseconds or more.

In one implementation, the power control circuit varies the voltage ofthe signal according to an exponential function, preferably anincreasing exponential function. Preferably the time constant of theexponential function is determined by the values of a resistor and acapacitor included in the power control circuit.

The electronic power switch may comprise a transistor, such as a fieldeffect transistor or a bipolar transistor. Preferably, the electronicpower switch comprises a MOSFET. If the electronic power switchcomprises a field effect transistor, the signal is applied to the gateof the transistor.

The flashlight may further comprise a microprocessor and a mechanicalswitch for opening and closing an electrical path between the powersource and the microprocessor. The microprocessor provides a controlsignal to the power control circuit in response to an activation signalreceived from the mechanical switch, and the power control circuitmodifies the control signal to produce the signal applied to theelectronic power switch. The voltage of the control signal preferablyvaries according to a step function when the flashlight is turned on,while the signal applied to the electronic power switch preferablyincreases over time according to an exponential function.

In another aspect of the present invention, the flashlight operates in aduty cycle of less than 11% in the “on” mode.

In another separate aspect of the present invention it is contemplatedthat elements of the aforementioned aspects of the present invention maybe combined.

Further aspects, objects, desirable features, and advantages of theinvention will be better understood from the following descriptionconsidered in connection with accompanying drawings in which variousembodiments of the disclosed invention are illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for the purpose of illustration only and are not intended as adefinition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a flashlight according to one embodimentof the present invention.

FIG. 2 is a cross-sectional view of the flashlight of FIG. 1 takenthrough the plane indicated by 2-2.

FIG. 3 is an enlarged cross-sectional view of the forward section of theflashlight of FIG. 1 taken through the plane indicated by 2-2.

FIG. 4 is a perspective view of the cross-sectional view shown in FIG.3.

FIG. 5 is a circuit diagram for the flashlight of FIG. 1 illustratingthe relationship of the electronic circuitry according to one embodimentof the invention.

FIG. 6 is a circuit diagram of one embodiment of a debounce circuit fora momentary switch that may be employed in a flashlight according to thepresent invention.

FIG. 7 is a circuit diagram of one embodiment of a microcontroller thatmay be employed in a flashlight according to present invention.

FIG. 8 is a circuit diagram of one embodiment of a power control circuitthat may be employed in a flashlight according to the present invention.

FIG. 9A is a circuit diagram of one embodiment of a short preventioncircuit according to the present invention.

FIG. 9B is a circuit diagram of one example of a power supply circuitfor a comparing device employed in short prevention circuit of FIG. 9A.

FIG. 10A shows three oscilloscope traces reflecting (1) how the voltageof a control signal from the microcontroller of the flashlight shown inFIG. 1 may vary over time when the flashlight is initially turned on,(2) how the voltage of a signal from the power control circuit varies inresponse to the control signal of the microcontroller, and (3) how thecurrent supplied to the lamp of the flashlight varies in response to thesignal from the power control circuit.

FIG. 10B shows three oscilloscope traces for a flashlight without apower control circuit according to the present invention, but wasotherwise the same as the flashlight used to obtain the oscilloscopetraces shown in FIG. 10A. The three traces shown in FIG. 10B reflect (1)how the voltage of a control signal from a microcontroller of aflashlight without a power control circuit may vary over time when theflashlight is initially turned on, (2) how the gate-to-source voltage ofthe electronic power switch will vary in response to the voltage of thecontrol signal, and (3) how the current supplied to the lamp of theflashlight varies in response to the voltage applied to the electronicpower switch.

FIG. 11A is an oscilloscope trace showing current flow over time in themain power circuit of a flashlight equipped with a power control circuitaccording to the present invention when the flashlight is initiallyturned on.

FIG. 11B is an oscilloscope trace showing current flow over time in themain power circuit of a flashlight without a power control circuitaccording to the present invention when the flashlight is initiallyturned on.

FIG. 12 shows three oscilloscope traces for a flashlight according tothe present invention that was operated in a strobe mode. The threetraces reflect: (1) the voltage of the control signal from themicroprocessor, (2) the voltage of the modified control signal generatedby the power control circuit, and (3) the current flow through theelectronic power switch.

FIG. 13 shows three oscilloscope traces for a flashlight according tothe present invention that was operated in a power reduction mode. Thethree traces reflect: (1) the voltage of the control signal from themicroprocessor, (2) the voltage of the modified control signal generatedby the power control circuit, and (3) the current flow through theelectronic power switch.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

To facilitate the description of the invention, any reference numeralrepresenting an element in one figure will represent the same element inany other figure.

A flashlight 10 according to one embodiment of the present invention isillustrated in perspective in FIG. 1. The flashlight 10 incorporates anumber of distinct aspects of the present invention. While thesedistinct aspects have all been incorporated into the flashlight 10, itis to be expressly understood that the present invention is notrestricted to flashlight 10 described herein. Rather, the presentinvention is directed to each of the inventive features of theflashlight described below individually as well as collectively.Further, as will become apparent to those skilled in the art afterreviewing the present disclosure, one or more aspects of the presentinvention may also be incorporated into other electronic devices,including cell phones, portable radios, toys, as well as othernon-portable lighting devices.

Referring to FIGS. 1-4, flashlight 10 includes a barrel 21 enclosed at arearward end by a tail cap 22 and at a forward end by a head and switchassembly 23.

Barrel 21 is preferably made out of aluminum. As is known in the art,barrel 21 may be provided with a textured surface 27 along its axialextent, preferably in the form of machined knurling.

In the present embodiment, barrel 21 is configured to enclose arechargeable lithium-ion battery pack 60. Battery pack 60 may compriseone or more lithium-ion battery cells. Preferably battery pack 60comprises at least two lithium-ion cells disposed physically in a seriesor end to end arrangement, while being electrically connected inparallel. In other embodiments, it may be desirable to electricallyconnect the two cells in series. Further, barrel 21 may also beconfigured to include a battery pack 60 comprising two or morelithium-ion batteries or cells physically disposed in a parallel orside-by-side arrangement, while being electrically connected in seriesor parallel depending on the design requirements of the flashlight.Furthermore, while a lithium-ion battery pack 60 is used as the powersource for the illustrated embodiment of flashlight 10, in otherembodiments of the present invention, other DC power sources may beemployed, including, for example, dry cell batteries as well as othertypes of rechargeable batteries.

The rechargeable lithium-ion battery pack 60 preferably includesbuilt-in short circuit protection circuitry 86, as best seen in FIG. 5.Battery packs of this type are readily available in the market from suchproviders as BYD Company Limited and will interrupt the flow of currentfrom the battery pack if the electrodes of the battery back are shortedtogether.

Tail cap 22 is also preferably made out of aluminum and is configured toengage mating threads provided on the interior of barrel 21 as isconventional in the art. However, other suitable means may also beemployed for attaching tail cap 22 to barrel 21. As best seen in FIG. 2,a one-way valve 68, such as a lip seal, may be provided at the interfacebetween the tail cap 22 and barrel 21 to provide a watertight seal.However, as those skilled in the art will appreciate, other forms ofsealing elements, such as an O-ring, may be used instead of one-wayvalve 68 to form a watertight seal. One way valve 68 is retained in acircumferential channel 70 formed in tail cap 22. Further one-way valve68 is oriented so as to prevent flow from outside into the interior ofthe flashlight 10, while simultaneously allowing overpressure within theflashlight to escape or vent to atmosphere.

The design and use of one-way valves in flashlights is more fullydescribed in U.S. Pat. No. 5,113,326 to Anthony Maglica, which is herebyincorporated by reference.

If made out of aluminum, the surfaces of barrel 21 and tail cap 22 arepreferably anodized with the exception of those surfaces used to makeelectrical contact with another metal surface for purposes of formingthe electrical circuit of the flashlight. In the present embodiment, anelectrical path is formed between barrel 21 and the case electrode 61 ofthe lithium-ion battery pack 60 by conductive member 72 and spring 74.In addition to forming part of the electrical path between the barreland case electrode, spring 74 also urges battery pack 60 forward so thatthe center electrode 63 of battery pack 60 is urged into one end ofspring biased conductor 76, which is held by and extends throughretaining bolt 57.

The head and switch assembly 23 of the present embodiment includes asupport structure 28 to which a number of other components may bemounted, including, for example, head 24, face cap 25, charging contact44, printed circuit board 46, sleeve 50, switch 52, and moveable lampassembly 100. For ease of manufacturing, support structure 28 ispreferably made out of injection molded plastic. Head 24, face cap 25,and sleeve 50, on the other hand, are preferably made from anodizedaluminum.

In the present embodiment, support structure 28 is a hollow supportstructure comprising a front section 31, a midsection 33 and an aftsection 35. The front section 31 comprises a generally cup-shapedreceiving area 37. The midsection 33, which extends rearward from thefront section 31, includes a generally cylindrical inner surface 39.And, the aft section 35, which extends rearward from the midsection 33,includes two opposing arcuate threaded fingers 55 (only one of which isvisible in the cross-sections of FIGS. 2-4).

The face cap 25 retains lens 26 and reflector 30 relative to the supportstructure 28. In the present embodiment face cap 25 is configured tothread onto external threads 29 provided on the front section 31 of thesupport structure 28. In other implementations, however, other forms ofattachment may be adopted. As illustrated, reflector 30 is positionedwithin the cup-shaped receiving area 37 of the front section 31 ofsupport structure 28. Corresponding alignment features 32, 34 may beprovided on the outer surface of reflector 30 and the internal matingsurface of support structure 28, respectively, to ensure properalignment between the reflector 30 and support structure 28.

Head 24 has a diameter greater than that of the barrel 21 and sleeve 50.Head 24 is also adapted to pass externally over the exterior of thebarrel 21 and sleeve 50. Internal surface 36 of head 24 is configured tomate with the outer surface 38 of support structure 28 at selectlocations to properly position head 24 relative to face cap 25 andsupport structure 28. A compressible retaining ring 40, such as a rubberO-ring, may be seated in a channel 41 extending around the outer surface38 of support structure 28 to create an interference fit between thesupport structure 28 and a feature provided on the internal surface 36of head 24, such as circumferential lip 42. Compressible retaining ring40 also prevents moisture and dirt from entering the head assemblybetween the support structure 28 and forward end of head 24.

External charging contacts 44 and 48 are provided at the forward sectionof flashlight 10. While charging contacts 44 and 48 are provided in thepresent embodiment in the form of charging rings to simplify therecharging procedure, in other embodiments contacts 44 and 48 may takeon other forms. In the present embodiment, printed circuit board 46 isinterposed between charging contacts 44 and 48. Printed circuit board 46is configured to be in electrical communication with charging contacts44 and 48, while simultaneously isolating charging contacts 44, 48 fromdirect electrical communication with one another through a shortcircuit. Electrical communication between printed circuit board 46 andcharging contacts 44, 48 may be established by providing a conductivetrace at the interface formed between printed circuit board 46 and eachof the charging contacts.

External charging contact 44 is preferably an aluminum ring disposed onthe external surface 38 of support structure 28, preferably toward theaft end of the mid-section 33. If barrel 21 is made out of anodizedaluminum, external charging contact 48 may be integrally formed inbarrel 21 by machining a portion of the barrel to remove any anodizingfrom the location of charging contact 48 or by masking the location ofcharging contact 48 prior to anodizing the barrel 21. In the presentembodiment, charging contact 48 is located at the forward end of barrel21.

As noted above, the head and switch assembly 23 also preferably includesa sleeve 50. Sleeve 50 is disposed over the external surface 38 of thesupport structure 28 so that it extends forward from the chargingcontact 44 to a position that is under the trailing edge 53 of head 24.Sleeve 50 is preferably made out of anodized aluminum, but may also bemade out of other metals or plastics. As a result of the foregoingconstruction, with the exception of the external surface formed byprinted circuit board 48 and switch 52, all of the external surfaces ofthe flashlight 10 according to the present embodiment may be made out ofmetal, and more preferably aluminum.

Sleeve 50 is provided with a hole 51 through which switch cover 54 ofswitch 52 extends. The outer surface of sleeve 50 surrounding switchcover 54 may be beveled to facilitate tactile operation of flashlight10. Sleeve 50 may also be provided with a groove 56 about itscircumference at a location forward of the trailing edge 53 of head 24for positioning a sealing element 58, such as an O-ring, to form awatertight seal between the head 24 and sleeve 50. Similarly, switchcover 54 is preferably made from molded rubber or latex. As bestillustrated in FIGS. 3 and 4, switch cover 54 is preferably configuredto prevent moisture and dirt from entering the head and switch assembly23 through hole 51.

In the present embodiment, lamp 59 is removeably mounted within the headand switch assembly 23 so as to extend into reflector 30 through acentral hole provided therein. In particular, lamp 59 is mounted onmoveable lamp assembly 100, which in turn is slideably mounted withinthe mid-section 33 of support structure 28.

While lamp 59 may be any suitable device that generates light, in thepresent embodiment lamp 59 is preferably an incandescent lamp bulb, andmore preferably a bi-pin incandescent lamp bulb. In otherimplementations of the invention, however, lamp 59 may comprise, forexample, an LED lamp or an arc lamp.

In the present embodiment, moveable lamp assembly 100 includes anadjustable ball housing 102, a ball-shaped adjustable bulb holder 104,an end cap 106, a retainer 108, retention spring 110, a spring biasedconductor 112, spring 114, conductor post 116 and cam follower assembly117.

As seen in FIGS. 3 and 4, lamp 59 is held by the ball-shaped adjustablebulb holder 104. The ball-shaped adjustable bulb holder 104 is in turnadjustably mounted within adjustable ball housing 102. In this regard,adjustable ball housing 102 is partially enclosed at its forward end bywall 103. Wall 103 includes a concave mating surface 118 against whichball-shaped bulb holder 104 is adjustably retained. Retainer 108, whichis adapted to slide within adjustable ball housing 102, includes aconcave surface 120 designed to slideably mate with the opposite side ofball-shaped adjustable bulb holder 104. End cap 106 encloses the aft endof adjustable ball housing 102 and is mounted in a fixed relationshipthereto. Retention spring 104 is interposed between the fixed end cap106 and the slideable retainer 108, thereby biasing retainer 108 towardthe forward end of the flashlight until concave surface 120 engagesball-shaped adjustable bulb holder 104. As a result, ball-shapedadjustable bulb holder 104 is adjustably held between concave surface118 of wall 103 and concave surface 120 of retainer 108.

Ball-shaped adjustable bulb holder 104 includes a metal portion 122, afirst contact holder 124, and a second contact holder 126. In thepresent embodiment, the metal portion 122 comprises a zone of a spherewith a through hole. First contact holder 124 and second contact holder126 are made from a non-conductive material, such as plastic, and areconfigured to create an interference fit within the through hole ofmetal portion 122. The second contact holder 126 includes a head portionshaped like a sector of a sphere so that in combination with the metalportion 122 the ball-shaped adjustable bulb holder 104 is provided witha substantially spherical outer surface.

The electrodes of lamp 59 extend into the first contact holder 122 wherethey preferably frictionally engage with positive and negative electrodecontacts, respectively (not shown). One of the electrode contacts, thenegative in the present embodiment, is configured to extend between themating surfaces of the first and second contact holders 124, 126 andmake electrical connection with the metal portion 122 of ball-shapedadjustable bulb holder 104. The other electrode contact, the positive inthe present embodiment, extends through both the first and secondcontact holders 124, 126 and includes a surface for mating with thespring biased conductor 112.

The construction of moveable lamp assembly 100 is described in detail inconnection with FIGS. 6-18 of pending U.S. patent application Ser. No.10/802,265, filed Mar. 16, 2004, which is hereby incorporated byreference.

The metal portion 122 of ball-shaped adjustable bulb holder 104 is inelectrical communication with adjustable ball housing 102, which is alsopreferably made out of metal. Adjustable ball housing 102 is in turn inelectrical communication with leaf spring conductor 128, a portion ofwhich is in slideable contact with the exterior of adjustable ballhousing 102. Leaf spring conductor 128 is also in electricalcommunication with printed circuit board 46 at contact pad 62 on printedcircuit board 46.

Contact post 116 extends through end cap 106 and switch housing 80.Contact post 116 is frictionally held by switch housing 80 so that itsaft end is in electrical communication with printed circuit board 46 atvia 64. Via 64 extends through the center of printed circuit board 46 inthe present embodiment. At its forward end, contact post 116 isslideably supported within the through hole provided in end cap 106. Acup-shaped portion 130 provided on the forward end of contact post 116is configured to hold one end of spring 114 while the other end ofspring 114 forces spring biased conductor 112 into contact with anexposed portion of the electrode contact extending through the secondcontact holder 126 of ball-shaped adjustable bulb holder 104. Springbiased conductor 112 is also cup-shaped in the present embodiment andhas a diameter slightly greater than that of cup-shaped portion 130 sothat it can slideably fit over the exterior surface of the cup-shapedportion 130 and hold spring 114 therebetween.

The head and switch assembly 23 is attached to barrel 21 by way of thetwo arcuate threaded fingers 55 forming the aft section 35 of supportstructure 28. The two arcuate threaded fingers 55 extend through printedcircuit board 46. The arcuate threaded fingers 55 are provided with bothexternal and internal threads. The external threads mate withcorresponding internal threads provided within the forward end of barrel21. Once the head and switch assembly 23 is threaded into the barrel 21,retaining bolt 57 is threaded into the internal threads of the arcuatethreaded fingers 55. Preferably the retaining bolt 57 includes a taperedshaft 59 configured to spread the arcuate threaded fingers 55, therebylocking the head and switch assembly 23 to the barrel.

Spring biased conductor 76 is compressibly held within central cavity 66of retaining bolt 57 between printed circuit board 46 and end wall 67.Spring biased conductor 76 also electrically couples via 64 on printedcircuit board 46 to center electrode 63 of rechargeable lithium-ionbattery pack 60.

FIG. 5 is a circuit diagram for flashlight 10 and schematicallyrepresents a preferred embodiment of the electronic circuitry accordingto the present invention. As shown in FIG. 5, flashlight 10 includes amain power circuit 400, a switch 52, a debounce circuit 500, amicroprocessor control circuit 600, a power control circuit 700,charging contacts 44, 48, and a short protection circuit 800. In thepresent embodiment, debounce circuit 500, microprocessor control circuit600, power control circuit 700, and short protection circuit 800 are allformed on printed circuit board 46. In other implementations, however,other arrangements are possible.

Main power circuit 400 of the present embodiment comprises, rechargeablelithium-ion battery pack 60, electrical path 402, lamp 59, electricalpath 404, and electronic power switch 702.

As best seen in FIG. 5, rechargeable lithium-ion battery pack 60includes built in short circuit protection circuitry 86. The built inshort circuit protection circuitry 86 is disposed in series withlithium-ion cell 88 within lithium-ion battery pack 60. In theillustrated embodiment, the short circuit protection circuitry isdisposed between the negative electrode of lithium-ion cell 88 and thenegative electrode of battery pack 60. Built-in short circuit protectioncircuitry 86 could, however, also be provided between the positiveelectrode of lithium-ion cell 88 and the positive electrode of batterypack 60.

Electrical path 402 connects the center electrode 63 of rechargeablelithium-ion battery pack 60 to the positive electrode of lamp 59. In theflashlight illustrated in FIGS. 1-4, electrical path 402 comprises thefollowing elements: spring biased conductor 76, via 64, conductor post116, spring 114, spring biased conductor 112, and the positive electrodecontact disposed within ball-shaped adjustable bulb holder 104.

Electrical path 402 connects the negative electrode of lamp 59 to thecase electrode 61 of the rechargeable lithium-ion battery pack. Further,electrical path 404 is opened and closed to complete and break the mainpower circuit 400 by electronic power switch 702, which is described inmore detail below. In the flashlight illustrated in FIGS. 1-4,electrical path 404 comprises: the negative electrode contact disposedwithin ball-shaped adjustable bulb holder 104, the metal portion 122 ofball-shaped adjustable bulb holder 104, adjustable ball housing 102,leaf spring conductor 128, contact pad 62, conductive trace 406,electronic power switch 702, conductive trace 408, barrel 21, conductivemember 72 in tail cap 22, and spring 74.

While electronic power switch 702 is located on printed circuit board 46in the present embodiment, electronic power switch 702 may also belocated in other places within flashlight 10.

Electronic power switch 702 is electrically coupled to contact pad 62via conductive trace 406, which is also provided on printed circuitboard 46. Electronic power switch 702 is also electrically coupled tobarrel 21 via conductive trace 408, which extends on printed circuitboard 46 from electronic power switch 702 to the interface betweenprinted circuit board 46 and barrel 21.

It is noted that other than electronic power switch 702, the constituentmembers of electrical paths 402, 404 are not critical to the operationof power circuit 400 according to the present aspect of the inventionand any combination of members as may be appropriate for forming theelectrical paths of a power circuit for a particular flashlight designmay be employed.

Electronic power switch 702 selectively opens and closes the electricalpath 404 between the lamp 59 and case electrode 61 of the rechargeablelithium-ion battery pack 60. When electronic power switch 702 is closed,current is permitted to flow through main power circuit 400.

The opening and closing of electronic power switch 702 is controlled, inthe present embodiment, by switch 52, microcontroller circuit 600 andpower control circuit 700.

Manipulation of switch 52 generates a signal which determines whetherelectronic power switch 702 opens or closes, or repeatedly opens andcloses in a manner hereinafter described.

In the present embodiment, switch 52 is a momentary switch. When switch52 is depressed, plunger 69 of switch 52 pushes snap dome 84 ofconductor 82 into electrical communication with conductor post 116. Asignal from battery pack 60 is then transmitted to printed circuit board46 through contact pad 65. When this signal is transmitted to printedcircuit board 46, electronic power switch 702 may be signaled to open orclose the electrical path 404, thereby permitting flashlight 10 to beturned on or off accordingly.

Unlike mechanical switches known in the art, switch 52 does not conductcurrent to the lamp 59. Instead, switch 52 merely provides an activationor deactivation signal. In the present embodiment, this activation ordeactivation signal is sent to microcontroller circuit 600, which inturn signals electronic power switch 702 through power control circuit700 to open or close accordingly. The main power circuit 400 in thepresent embodiment is thus indirectly activated or deactivated by themanipulation of switch 52 by a user.

Because the current from rechargeable lithium-ion battery pack 60 to thelamp 59 passes through electronic power switch 702, and not switch 52,switch 52 may be designed to operate under very low current.

In the illustrated embodiment shown in FIG. 5, switch 52, debouncecircuit 500, microcontroller circuit 600, power control circuit 700, andelectronic power switch 702 are all in electrical communication. Whenswitch 52 is initially depressed, a signal is sent to themicrocontroller circuit 600 through the debounce circuit 500. Themicrocontroller circuit 600 in response sends a signal through the powercontrol circuit 700 to the electronic power switch 702. In response, theelectronic power switch 702 permits current to flow to lamp 59 from thelithium-ion battery pack 60 at a controlled increasing rate over apredetermined period. A more detailed description of debounce circuit500, microcontroller circuit 600, power control circuit 700, andelectronic power switch 702 are discussed below in connection with FIGS.6, 7, and 8.

FIG. 6 is a detailed schematic of one embodiment of a debounce circuit500 that may be employed in the present invention. Debounce circuit 500may be used to reduce the noise, current, and voltage of the signal sentfrom switch 52 to the microcontroller circuit 600.

A signal to turn lamp 59 on or off enters the debounce circuit 500through contact pad 65 when a user manipulates switch 52 in a manner soas to cause plunger 69 to force snap dome 84 into contact with conductorpost 116. As a result of this manipulation, a signal is sent via contactpad 65 through debounce circuit 500. The output of the debounce circuit500 is provided at output 507, which is in electrical communication withmicrocontroller circuit 600 illustrated in FIG. 7.

In one embodiment of debounce circuit 500, capacitors 502, 504, 505, andresistor 503 are coupled in parallel to contact pad 65 and output 507,while resistor 506 is serially interposed between contact pad 65 andoutput 57, preferably down stream of the parallel branches for capacitor502 and resistor 503.

Those skilled in the art will know how to design a debounce circuit 500to achieve a suitable signal level to microcontroller circuit 600. Inthe design illustrated in FIG. 6, however, it has been found thatresistor 506 may have a resistance of 10 KΩ, resistor 503 may have aresistance of 1 KΩ and capacitors 502, 504, and 505 may each have acapacitance of 0.1 μF.

FIG. 7 is a schematic diagram of microcontroller circuit 600. In thepresent embodiment, microcontroller circuit 600 includes amicrocontroller 601 having an input 602 and two outputs 604, 606.Further, the GND pin of microcontroller 601 is directly connected toground, and the Vcc pin of the microcontroller 601 is electricallyconnected to battery pack 60 via conductive trace 608 and to groundthrough capacitor 610 via conductive trace 612. The signal provided ontrace 608 may also be a battery signal that has been filtered by adiode, although such filtering is unnecessary. If such filtering isperformed, it may be performed in the short protection circuit 800 asdescribed below.

A signal from output 507 of the debounce circuit 500 entersmicrocontroller 601 through input pin 602. Microcontroller 601 may beprogrammed to provide for different user selectable functions, theselection of which may be controlled by the nature of the input signalreceived on input pin 602. Thus, for example, if flashlight 10 is in theoff state and switch 52 is depressed and released, microcontroller 601may be programmed to provide a signal on output pin 606 that will turnflashlight 10 on. Microcontroller 601 may further be programmed so thatthe flashlight 10 will stay on with a second depression of switch 52until the second release of switch 52. Other functions may also beprogrammed into microcontroller 601. For example, microcontroller 601may be programmed such that a user may select a power reduction mode bydepressing switch 52 and holding it down for two seconds or a strobemode by depressing switch 52 and holding for 4 seconds. Other functionalmodes that can be performed by microcontroller 601 may include a beaconfunction mode and an automatic off mode.

If flashlight 10 is in the off state, microcontroller 601 will send acontrol signal out through output pin 606 in response to a signalreceived through input pin 602. The control signal from output pin 606is provided to input 707 of power control circuit 700 where it ismodified in a desired manner before being supplied over trace 708 toelectronic power switch 702 so that electronic power switch 702 isgradually closed in response to the control signal, thereby limiting theinitial in-rush of current through lamp 59.

In connection with other operational modes programmed intomicrocontroller 601, it may be desirable to modify the control signalproduced by microcontroller 601 in an alternative manner. Accordingly,in the illustrated embodiment, microcontroller 601 also includes asecond output 604 for providing a second control signal to power controlcircuit 700. A control signal from output pin 604 is provided to input709 of power control circuit 700. The control signal from output pin 604is modified within power control circuit 700 before being provided ontrace 708 to electronic power switch 702 so that power switch 702 isclosed at a different rate in response to a control signal provided onoutput pin 604 of microcontroller 601.

FIG. 7 is a schematic diagram of power control circuit 700, which iscoupled to electronic power switch 702 via conductive trace 708. Anelectronic power switch 702 is selected that permits different levels ofcurrent to flow through main power circuit 400 in response to differentsignal levels provided at trace 708. In the present embodiment,electronic power switch 702 comprises an n-channel MOSFET 705. The gateof the MOSFET is electrically connected to trace 708, the drain to thecenter electrode 63 of battery pack 60 through input 703, and the sourceto ground (e.g., the case electrode 61 of battery pack 60). An n-channelMOSFET works well in the present invention due to its transfercharacteristics, namely that the drain current is zero (i.e., theelectronic power switch 702 is open) when the gate-to-source voltage isbelow approximately 0.75 Volts.

While the present embodiment employs an n-channel MOSFET 705, it willbecome apparent to those skilled in the art from the present disclosurethat other types of electronic power switches may also be employed inthe present invention. For example, a p-channel MOSFET could be used inplace of the re-channel MOSFET if electronic power switch 702 wereprovided on the high-side of main power circuit 400 (i.e., prior to lamp59). Similarly, other types of transistors may also be employed forelectronic power switch 702, including other field effect transistors,such as JFETs and DE MOSFETs, and bipolar junction transistors.

As noted above, power control circuit 700 modifies the control signalsreceived from output pins 604, 606 of microcontroller 601. Inparticular, power control circuit 700 is designed to modify the controlsignals so that they vary over time based on the transfercharacteristics of the employed electronic power switch 702 and the rateat which electronic power switch 702 is to be closed. Preferably, powercircuit 700 modifies at least one of the control signals received frommicrocontroller 601 so that when the control signal reaches electronicpower switch 702, electronic power switch 702 is gradually closed overtime, as opposed to being closed instantaneously.

When flashlight 10 is in the off state, the signals at inputs 707 and709 are both high impedance signals so they are effectively not part ofpower control circuit 700. Further, the value of resistor 703 isselected so that when flashlight 10 is in the off state, resistor 703pulls the gate voltage of MOSFET 705 to zero volts (through resistor701) so that electronic power switch 702 is open.

The degree to which electronic power switch 702 is closed and hence theamount of current permitted to flow in main power circuit 400 isultimately controlled in the illustrated embodiment by the voltageacross capacitor 710, which also correspond to the gate-to-sourcevoltage of MOSFET 705. When a control signal is provided on inputs 707or 709, the voltage across capacitor 710 will increase exponentiallyaccording to the equation V_(c)=E(1−e^(−t/τ)) until the maximum voltageof the control signal is achieved. In the foregoing equation, E is thevoltage of the control signal applied to input 707 or 709 and τ is thetime constant for the circuit and is determined by the equation τ=RC.Further, while it takes a period of approximately 5τ before a capacitoris fully charged, during a period of 1τ the voltage across capacitor 710will reach approximately 63% of the voltage of the applied controlsignal from microcontroller 601. Thus, by appropriately selecting R andC for each of the circuit paths corresponding to inputs 707 and 709, therate at which the gate-to-source voltage increases, and hence howquickly the electronic power switch 702 is closed, after a controlsignal is provided from microcontroller 601, may be controlled.

As noted above, when flashlight 10 is initially turned on, a controlsignal is provided from output pin 606 of microcontroller 601 to input707 of power control circuit 700. As a result, the signal at input 707goes from high impedance to, for example, a 3 Volt signalinstantaneously. The voltage across capacitor 710, and hence thegate-to-source voltage will, however, increase exponentially to 3 Voltsaccording to the formula given above. By gradually increasing thevoltage of the control signal to reach electronic power switch 702 overtrace 708 in the foregoing manner, the current permitted to flow to lamp59 may be increased at a controlled rate. In turn, by increasing theamount of current sent to lamp 59 at a controlled rate, lamp 59 may bepermitted to achieve its steady state resistance at a controlled,reduced rate, thereby protecting lamp 59 from the normal large initialsurge of current from battery pack 60 when the flashlight is turned on.

In a preferred embodiment, resistor 701 has a resistance of 470 KΩ,resistor 703 has a resistance of 1 KΩ and capacitor 710 has acapacitance of 0.1 μF. This combination of resistor 701 and capacitor703 forms a low pass filter with a time constant of 47 ms(470,000×0.000001=0.047 seconds or 47 milliseconds). During this periodcapacitor 710 will be charged to approximately 63% of the voltage of thecontrol signal provided on input 707 (or 0.63*5 Volts=3.15 Volts). Thismeans that it will take approximately 47 ms for the gate-to-sourcevoltage of MOSFET 705 to pass from the off region, through the currentlimited region, to the linear region of the transistor. During thistime, the filament of lamp 59 is heated while limiting the in-rush ofcurrent to a more desirable level.

As noted above, a control signal provided on output 604 ofmicrocontroller 601 may be provided to input 709 for purposes of closingelectronic power switch 702 at a different rate than that achieved by acontrol signal provided at input 707. For example, resistor 704 may beset at 1.0 KΩ, while capacitor 710 is still set at a capacitance of 0.1μF. This combination results in a low pass filter circuit with a timeconstant of 0.0001 seconds (0.1 ms). Thus, under this configuration,capacitor 710 will be charged to approximately 63% of the voltage of thecontrol signal provided at input 709 (or 3.15 Volts in the presentembodiment) in 0.1 ms.

Accordingly, a control signal provided on input 709 of power controlcircuit 700 may be used to close and open electronic power switch 702 atmuch higher frequency than a control signal provided on input 707. Thisfeature may be desirable for certain user selectable functions, such asa power reduction mode. For example, if a user selects a power reductionmode by depressing switch 52 for an appropriate duration, themicrocontroller 601 may send out an initial control signal from outputpin 606 to input 707 to energize lamp 59 relatively slowly as describedabove. After the lamp 59 has already been turned on and the filament hasbeen heated so that it is at or near its steady state resistance,microcontroller 601 may send out a square wave pulse modulated controlsignal, such as the one shown in FIG. 13, from output pin 604 to input709 of power control circuit 700 and stop sending out a control signalon output 606.

Based on a time constant of 0.1 ms, the pulse modulated signal sent outfrom output pin 604 of microcontroller 601 could be modulated at a ratebetween approximately 5 kHz and 100 Hz, and still be at a frequency thatis much higher than the visible flicker rate of 60 Hz. Further, due tothe short cycle time between each pulse, the filament of lamp 59 willnot cool sufficiently between cycles so as to result in undue stress bythe high frequency of the on, off cycles. As a result, flashlight 10 maybe operated in a manner that will permit lamp 59 to, for example,operate at half power and thus consume half the energy it would normallyconsume over a given period of time.

Although the power control circuit of the present embodiment has beendescribed as employing an RC circuit to modify the control signalprovided to electronic power switch 702, other forms of circuits withtime constants, such as RL and RLC circuits, may be employed in powercontrol circuit 700 as well. In addition, circuits that produce linear,sinusoidal, saw tooth, or triangular waveforms may also be used forpower control circuit 700. Further, the benefits of power controlcircuit 700 may be realized in a flashlight in which the control signaldelivered to the power control circuit comes directly from a mechanicalswitch as opposed to a microcontroller or in which any form of DC powersource is substituted for battery pack 60.

FIG. 10A graphically demonstrates the beneficial dampening effects thatpower control circuit 700 may provide to lamp 59 when flashlight 10 isinitially turned on. In contrast, FIG. 10B graphically demonstrates thatthe rate of change of current flow and the peak current flow throughelectronic power switch 702 is much greater when a power control circuit700 according to the present invention is not controlling the signal toelectronic power switch 702.

FIG. 10A shows three oscilloscope traces 1002, 1004, 1006. Theoscilloscope traces of FIG. 10A were obtained from a flashlight having apower control circuit 700 as described above in connection with FIG. 8to drive an electronic power switch 702 comprising a MOSFET 705.Further, the resistor 701 had a value of 470 KΩ and the capacitor 710had a value of 0.1 μF. The time constant for the power control circuitwas thus 47 ms.

The oscilloscope traces of FIG. 10B were obtained at a time when theflashlight went from the off state to the on state and respectivelyreflect (1) how the voltage of the control signal from themicrocontroller 601 of the flashlight varied over time when theflashlight was initially turned on, (2) how the voltage of the signalfrom the power control circuit 700, and hence the gate-to-source voltageof MOSFET 705, varied in response to the control signal of themicrocontroller, and (3) how the current that traveled through MOSFET705, and hence supplied to the lamp 59 of the flashlight, varied inresponse to the signal from the power control circuit.

The x-axis of FIG. 10A represents time in milliseconds, and the distancebetween each of the vertical grid lines crossing the x-axis represents40 milliseconds. The y-axis of FIG. 10A, on the other hand, representsdifferent units or values depending on which signal or curve is beingreferenced.

In FIG. 10A, trace 1002 is an oscilloscope trace of the voltage of thecontrol signal output from microcontroller 601 when the flashlight 10was initially turned on. The spacing between each of the grid linescrossing the y-axis for trace 1002 represent 2 Volts. As illustrated inthe graph, the voltage of control signal 1002 basically corresponded toa step wave. Hence, the voltage of the control signal went from a lowcondition of 0 Volts to a high condition of 3 Volts when flashlight 10was turned on.

Trace 1004 is an oscilloscope trace of the voltage of the control signaloutput from microcontroller 601 after it passed through power controlcircuit 700 via input 707. Thus, it corresponds to the gate-to-sourcevoltage of MOSFET 705. As with signal 1002, the spacing between each ofthe grid lines crossing the y-axis represents 2 Volts for trace 1004.The voltage of this modified control signal exhibits an exponentialgrowth function as discussed above. This exponential increase in thevoltage of the signal sent to electronic power switch 702 closed powerswitch 702 at a controlled rate. Hence, the rate of change of currentflow and the peak current flow through MOSFET 705 and lamp 59 wasreduced. This can be seen by comparing trace 1006 to corresponding trace1012 shown in FIG. 10B, both of which are discussed below.

Trace 1006 of FIG. 10A is an oscilloscope trace of the current flowthrough MOSFET 705, and hence lamp 59, that resulted from thegate-to-source voltage being controlled in the manner illustrated bytrace 1004. The spacing between each of the grid lines crossing they-axis represents 2 Amps for trace 1006. FIG. 11A shows trace 1006, butat an increased time scale. The time scale used in FIG. 11A is ten timesgreater than that used in FIG. 10A; thus, the space between each of thevertical grid lines in FIG. 11A represents 4 milliseconds. The currentscale on the y-axis for FIG. 11A, on the other hand, is the same as thatfor trace 1006 in FIG. 10A.

The peak current that was permitted to flow through lamp 59 when theflashlight 10 was turned on was determined to be 3.75 Amps in thisexample of the present invention. The peak current may be determinedfrom curve 1006 shown in FIGS. 10A and 11A by measuring the height ofthe current peak in curve 1006 relative to its baseline. Because FIG.11A shows current flow through MOSFET 705 at a time scale greater thanthat shown in FIG. 10A, however, a more accurate measurement of the peakcurrent can be made from FIG. 11A.

FIG. 10B shows three oscilloscope traces 1008, 1010, 1012. Theflashlight used to obtain the traces of FIG. 10B. was the same as theflashlight used to obtain the oscilloscope traces shown in FIG. 10A,except that it was modified so that the control signal frommicroprocessor 601 was fed directly into the gate of MOSFET 705, thusbypassing the power control circuit according to the present invention.As with FIG. 10A, the oscilloscope traces shown in FIG. 10B were takenat a time when the flashlight went from the off state to the on stateand respectively reflect (1) how the voltage of the control signal fromthe microcontroller of the flashlight varied over time when theflashlight was initially turned on and the control signal was feddirectly into the gate of MOSFET 705, thus bypassing the power controlcircuit 700, (2) how the gate-to-source voltage of MOSFET 705 varied inresponse to the voltage of the control signal under such circumstances,and (3) how the current that flowed through the electronic power switch,and hence supplied to the lamp of the flashlight, varied in response tothe voltage applied to the gate of electronic power switch.

The x-axis of FIG. 10B represents time in milliseconds, and the distancebetween each of the vertical grid lines crossing the x-axis represents40 milliseconds. The x-axis, therefore, employs the same scale as usedin FIG. 10A. The y-axis of FIG. 10B, like the y-axis of FIG. 10A,represents different units or values depending on which signal or curveis being referenced.

In FIG. 10B, trace 1008 is an oscilloscope trace of the voltage of thecontrol signal output from microcontroller 601 when the flashlight wasinitially turned on. The spacing between each of the grid lines crossingthe y-axis for trace 1002 represent 2 Volts like in FIG. 10A. Asdemonstrated in the graph, the voltage of control signal 1002 basicallycorresponds to a step wave. Hence, the voltage of the control signalwent from a low condition of 0 Volts to a high condition of 3 Volts whenflashlight 10 was turned on. Notably, however, the leading edge ofcontrol signal 1008 is slightly rounded. This is the result of the largein-rush of current that occurred through lamp 59 of the comparativeexample at the instant the flashlight was turned on. This in-rush ofcurrent effectively lowered the voltage of the battery pack momentarily.A similar dip in the voltage of the control signal is observed in curve1002. However, in curve 1002, the dip is displaced from the leading edgeof the control signal and it is not as large. This is because the peakcurrent flow through lamp 59 is delayed and reduced in the flashlightemploying a power control circuit 700 according to the presentinvention.

Trace 1010 is an oscilloscope trace of the gate-to-source voltage ofMOSFET 705. As with signal 1008, the spacing between each of the gridlines crossing the y-axis represents 2 Volts. In the present comparativeexample, the gate-to-source voltage is the same as the voltage of thecontrol signal 1008 provided by the microcontroller because the powercontrol circuit for the flashlight was bypassed. As a result of therebeing no power control circuit 700 interposed between microcontroller601 and electronic power switch 702, power switch 702 wasinstantaneously driven from a state of non-conduction to a location onthe transfer characteristics curve of MOSFET 705 that would permitsignificantly more current to flow through MOSFET 705 than actuallyflows through main power circuit 400. In other words, the rate of changeof current flow and the peak current flow through main power circuit 400was not limited by power switch 702 while transitioning the flashlightfrom the off state to the on state. This in turn resulted in the largein-rush of current to lamp 59 and the large current spike observed intrace 1012 of FIG. 10B.

Trace 1012 of FIG. 10B is an oscilloscope trace of the current flowthrough MOSFET 705, and hence lamp 59, versus time when thegate-to-source voltage is not controlled by a power control circuit. Thespacing between each of the grid lines crossing the y-axis represents 2Amps for trace 1012. FIG. 11B shows trace 1012, but at an increased timescale. The time scale used in FIG. 11B is ten times greater than thatused in FIG. 10B; thus, the space between each of the vertical gridlines in FIG. 11B represents 4 milliseconds and FIG. 11B is on the sametime scale as FIG. 11A. The current scale on the y-axis for FIG. 11B, onthe other hand, is the same as that for trace 1012 in FIG. 10B as wellas that for trace 1006 in FIG. 11A.

The peak current flow through MOSFET 705 and lamp 59 for this comparisonexample was approximately 7.8 Amps. A comparison of curve 1006 in FIGS.10A and 11A to curve 1012 in FIGS. 10B and 11B thus shows that the peakcurrent delivered to the lamp 59 was reduced by approximately 4.05 Amps,or by slightly more than 50%, when the power control circuit 700according to the above described example of the invention was employedto control the rate at which electronic power switch 702 was closed. Acomparison of curves 1006 and 1012 also shows that that the current peakin curve 1006 is much broader and softer than the current peak in curve1012. This results from the fact that the rate of change of current flowthrough electronic power switch 702 may be markedly reduced inflashlights employing a power control circuit 700 according to thepresent invention.

It is to be recognized that the current curve 1006 shown in FIGS. 10Aand 11A is merely one example of how current to lamp 59 may becontrolled. Indeed, if a power control circuit 700 with different timeconstants or characteristics, an electronic power switch 702 withdifferent transfer characteristics, or a lamp having differentcharacteristics is employed, a different curve may result, thuseffecting the amount of the dampening effect achieved.

The oscilloscope traces of FIG. 12 were obtained from the sameflashlight used to obtain FIG. 10A. The flashlight, however, was beingoperated in the strobe mode when the oscilloscope traces 1002, 1004, and1006 of FIG. 12 were recorded. The strobe mode was selected by holdingswitch 52 down for approximately 4 seconds, thus providingmicroprocessor 601 an activation signal for the strobe mode.

As with FIG. 10A, traces 1002, 1004, and 1006 of FIG. 12 correspond,respectively, to the voltage of the control signal from output pin 606of microprocessor 601, the voltage of the modified control signalgenerated by the power control circuit 700, and the current throughMOSFET 705. The y-axis scale for each of curves 1002, 1004, and 1006corresponds to the y-axis scale for the corresponding curves of FIG.10A. However, the scale of the x-axis in FIG. 12 is one-tenth the scalethat was used in FIG. 10A; thus, the spacing between each of thevertical gridlines in FIG. 12 corresponds to 400 milliseconds. A reducedscale was used so that a series of strobe cycles could be observed.

As shown in FIG. 12, the voltage of the control signal 1002 wasmodulated according to a square wave during strobe mode operation. Eachcycle of the square wave equaled approximately 1.6 seconds. During onehalf of the cycle, the voltage of the control signal was approximately3.6 Volts, while during the other half the cycle the voltage of thecontrol signal was 0 Volts. The 800 milliseconds between each on cycle,was much greater than the time required for the filament of lamp 59 tocool, and again act like a short circuit when initially powered.

Trace 1004 is an oscilloscope trace of the voltage of the control signaloutput from microcontroller 601 after it had passed through powercontrol circuit 700 via input 707, and thus corresponds to thegate-to-source voltage of MOSFET 705. The voltage of this modifiedcontrol signal exhibits an exponential growth function at the leadingedge of each pulse and an exponential decay function at the trailingedge of each pulse. The exponential growth function is due to the 47 mstime constant of the RC circuit formed by the resistor 701 and capacitor710 combination. The exponential decay function will also have a timeconstant of approximately 47 ms, because resistor 703 is only 1 KΩ.

Because the voltage of the signal 1004 provided to electronic powerswitch 702 increased exponentially at the leading edge of each pulse inthe same manner as signal 1004 in FIG. 10A increased, power switch 702was closed at the same controlled rate described above in connectionwith FIG. 10A. Indeed, if the time scale of FIG. 12 were to be increasedto that used in FIG. 10A or 11A, the leading edge of each current pulseshown in trace 1006 of FIG. 12 would look the same as the leading edgeof the current pulses in traces 1006 of those figures. The rate ofchange of current flow and the peak current flow through MOSFET 705 andlamp 59 were, therefore, reduced each time the lamp was powered duringthe strobe mode, thus reducing the stresses placed on the filament oflamp 59 each time the lamp was powered during a cycle. This was so eventhough the filament cooled during the “off” portion of each cycle to atemperature that again made the filament behave like a short circuit.

Because the stresses placed on the filament of the lamp are reduced eachtime the lamp is powered in a flashlight having a power control circuitaccording to the present invention, the lamp will have an extended lifeexpectancy. This is particularly beneficial when the flashlight isoperated in a strobe mode where the stresses placed on the lamp filamentquickly accumulate with each pulsing of the lamp.

It can be seen from FIG. 12 that current continues to flow through lamp59 even after control signal 1002 has switched from a high state to alow state. This is because the trailing edge of each pulse in trace 1004exhibits an exponential decay function. Thus, electronic power switch702 will continue to conduct current until the voltage of the modifiedcontrol signal drops below a level sufficient to permit MOSFET 705 toconduct. Because the time constant of the decay path for power circuit700 was approximately 47 ms in the present example, MOSFET 705 continuedto conduct current for approximately 40 to 50 ms after each time thecontrol signal 1002 went from the high state to the low state.

FIG. 13 illustrates the operation of flashlight 10 of the illustratedembodiment in a power reduction mode. The power reduction mode wasselected by holding switch 52 down for approximately 2 seconds. FIG. 13shows three oscilloscope traces 1014, 1016, 1018. The oscilloscopetraces of FIG. 13 were obtained from a flashlight having a power controlcircuit 700 as described above in connection with FIG. 8 to drive anelectronic power switch 702 comprising a MOSFET 705. The resistor 701had a value of 470 KΩ, the resistors 703 and 704 had a value of 1 KΩ andthe capacitor 710 had a value of 0.1 μF. Thus, the time constantcorresponding to input 707 of the power control circuit 700 was 47 mswhile the time constant for input 709 was 0.1 ms.

The oscilloscope traces of FIG. 13 were obtained at a time when theflashlight switched from the normal “on” state to a power reduction modeand respectively reflect (1) how the voltage of a control signal of themicrocontroller 601 of the flashlight shown in FIG. 1 may vary over timewhen the flashlight is operated in the power reduction mode, (2) how thevoltage of the signal from the power control circuit 700, and hence thegate-to-source voltage of MOSFET 705, varied in response to the controlsignal of the microcontroller, and (3) how the current that traveledthrough MOSFET 705, and hence supplied to the lamp 59 of the flashlight,varied in response to the signal from the power control circuit.

The x-axis of FIG. 13 represents time in milliseconds, and the distancebetween each of the vertical grid lines crossing the x-axis represents40 milliseconds. The y-axis of FIG. 13, however, represents differentunits or values depending on which signal or curve is being referenced.

Trace 1014 is an oscilloscope trace of the voltage of the control signalthat was output from output pin 604 of microcontroller 601 as theflashlight 10 transitioned from a normal “on” mode to a power reductionmode. The flashlight was initially turned on by sending out a controlsignal from output pin 606 to input 707 of power control circuit 700 toenergize lamp 59 relatively slowly as described above. Once the lampreached a steady state, however, microcontroller ceased outputting thecontrol signal on output pin 606 and began outputting the control signalfrom output pin 604 to input 709 of power control circuit 700. The timeperiod reflected in the oscilloscope traces of FIG. 13 is after thistransition had occurred.

The spacing between each of the grid lines crossing the y-axis for trace1014 represent 2 Volts. Thus, as seen from FIG. 13, prior totransitioning to the power reduction mode, the voltage of control signal1014 was at a steady state of approximately 3 Volts. After theflashlight transitioned to the power reduction mode, the voltage ofcontrol signal 1014 corresponded to a square wave. Each cycle of thesquare wave equaled approximately 8 milliseconds. During one half of thecycle, the voltage of the control signal was approximately 3.6 Volts,while during the other half the cycle the voltage of the control signalwas 0 Volts.

Trace 1016 is an oscilloscope trace of the voltage of the control signalafter passing through power control circuit 700 via input 709. Trace1016 also corresponds to the gate-to-source voltage of MOSFET 705.

As with signal 1014, the spacing between each of the grid lines crossingthe y-axis represents 2 Volts for trace 1016. Because the control signal1014 passed through a portion of power control circuit 700 that had avery small time constant of 0.1 ms, the voltage of the modified controlsignal shown by curve 1018 tracks very closely to that of the controlsignal.

Trace 1018 of FIG. 13 is an oscilloscope trace of the current flowthrough MOSFET 705, and hence lamp 59, that resulted from thegate-to-source voltage being controlled in the manner illustrated bytrace 1016. The spacing between each of the grid lines crossing they-axis represents 2 Amps for trace 1016.

From curve 1018, it is observed that during the “on” portion of eachcycle, no current spike is observed. Rather, the current through MOSFET705 and lamp 59 returns to the steady state level of approximately 1 Ampeach time signal 1016 goes to the high condition. This is because thefilament is not powered only about 4 ms out of each cycle. This isinsufficient for the filament of lamp 59 to cool to the point that itagain acts like a short circuit. Because the lamp is driven at a rate ofapproximately 125 Hz, the human observer will not perceive anyflickering in lamp 59, although lamp 59 will appear dimmer.

Lamp 59 will appear dimmer because lamp 59 is being operated at half itsnormal steady state power. The peak power of the flashlight during thepower reduction mode is the same as that when the flashlight is operatedin the normal mode. However, because the lamp is only powered for halfof each cycle during the power reduction mode, its average power will behalf its peak power. Further, the lamp will only consume half the energyit consumes during normal operation.

Notably, the trailing edge of each pulse in trace 1016 does not exhibitan exponential decay function corresponding to a time constant of 47 msas seen with pulses 1004 in FIG. 12. This is because capacitor 710 isnot drained through resistor 703 when the flashlight is operated inpower reduction mode. Instead, when the flashlight is operated in thepower reduction mode, another path to ground is provided throughmicrocontroller 601, thus keeping the time constant of the decayfunction for input 709 at about 0.1 ms. This alternative path to groundis necessary if it is desired to drive lamp 59 at a rate of more thanapproximately 10 Hz, which is about the limit of the decay path throughresistors 701, 703 based on the resistance values used in the presentexample and significantly below the 125 Hz at which lamp 59 was actuallydriven in the illustrated example.

The beacon mode will now be described. The flashlight may be placed inthe beacon function mode, for example, by holding switch 52 down for aspecific time or by depressing the switch 52 multiple times, thusproviding microprocessor 601 an activation signal for the beacon mode.

In the beacon function mode, the microcontroller 601 is programmed in away such that the flashlight lamp 59 comes on for a short period of timeand then goes off for a longer period of time. The voltage of thecontrol signal from output pin 606 of microprocessor 601 may be a stepfunction that facilitates the flashlight lamp 59 to be repetitivelycycled to come on for 0.03-0.25 seconds and then off for 1.2-2 seconds.Alternatively, the flashlight lamp 59 can be repetitively cycled to comeon for 50 milliseconds and then off for 1.33 seconds. In this way, thebeacon mode results in an eye-catching flash that is suitable forsignaling, for example, the location of the flashlight holder to arescuer or police officer in a time of need.

The period of the cycle during the beacon mode is not limited to amaximum of 2.25 seconds and may be up to five seconds or more, asdesired. In the beacon mode according to the disclosed embodiment,during the “on” portion of the cycle, the voltage of the control signalis in the high condition, while during the “off” portion of the cyclethe voltage of the control signal is 0 volts. Cycling the control signalin this way results in a great conservation of battery energy. Forexample, when the flashlight is operating in the beacon mode, the dutycycle is 0.05/1.38, or 3.6% in the “on” mode. In such a case, an energyconsumption reduction of about 96% compared to a steady-on lamp can beachieved. A reduction in energy consumption is also achieved under otherduty cycle ranges, e.g., at approximately 1.4% duty cycle or 30milliseconds “on” and 2 seconds “off,” or at approximately 17.2% dutycycle or 0.25 seconds “on” and 1.2 seconds “off.” Those skilled in theart will recognize that this energy consumption benefit may be achievedindependent of the type of lamp 59. Thus, this benefit can be realizedwhether the light source is an LED or a filament based lamp.

The beacon mode may further be implemented with the power controlcircuit 700 by having the control signal from output pin 606 connect toinput 707 or 709 as illustrated in FIG. 8. The “off” time during thebeacon mode is sufficiently long to allow the filament of the flashlightlamp 59 to cool. Thus, modifying the control signal, for example, viathe power control circuit 700 such that the signal provided to theelectronic power switch 702 is increased exponentially serves to reducethe stresses placed on the filament of the lamp 59. In this way, thelamp will have an extended life expectancy in addition to the reductionin energy consumption advantageously facilitated by the beacon mode asdescribed above.

Another and distinct aspect of the present invention relates toproviding an improved short protection circuit for exposed chargingcontacts.

As best seen from FIGS. 1 and 5, charging contacts 44 and 48 serve asthe interface between a recharging unit and rechargeable lithium-ionbattery pack 60 of flashlight 10. Although not depicted here, it will beappreciated that the cradle of the recharging unit should be fashionedin a way to make electrical contact with the external charging contacts44 and 48 and hold flashlight 10 in place while charging takes place.Because charging contacts 44 and 48 extend around the entire externalcircumference of flashlight 10, however, a recharging unit having asimple cradle design may be used. For example, a cradle design thatpermits flashlight 10 to be placed into the recharging unit in anyradial orientation relative to its longitudinal axis and still be ableto make contact with the recharging unit's charging contacts may beused. Thus, flashlight 10 does not need to be pressed into the chargingunit so that hidden plugs or tabs can be inserted into the flashlight inorder to make contact with the charging contacts of the recharging unit.

Because charging contacts 44 and 46 are externally exposed, however,there is a potential that they become shorted by a metal object in theuser's hands during operation. To avoid tripping the short circuitprotection circuitry 86 provided in lithium-ion battery pack 60 in suchcircumstances, a short protection circuit 800 is preferably electricallyinterposed between at least one of the charging contacts 44, 48 and therechargeable lithium-ion battery pack 60.

In the embodiment illustrated in FIG. 5, charging contact 44 iselectrically connected to short protection circuit 800, which in turn isconnected to electrical path 402 and center electrode 63 of battery pack60 by way of conductor 821 and via 64. Charging contact 48 is alsocoupled to short protection circuit 800. In addition, it is connectedvia barrel 21, conductive member 72 and spring 74 to case electrode 61of battery pack 60.

While in the present embodiment, short protection circuit 800 is locatedon printed circuit board 46, short protection circuit 800 could bephysically located at any suitable location within flashlight 10.

The short protection circuit 800 operates to create an open circuitbetween the battery pack 60 and at least one of the charging contacts44, 48 if a short is detected between charging contacts 44 and 48. Thus,flashlight 10 may be operated safely without fear that an inadvertentshort across charging contacts 44, 48 will interrupt the flow of currentfrom battery pack 60 to lamp 59 during operation of the flashlight.

A detailed description of one embodiment of a short protection circuit800 is described in connection with FIGS. 9A and 9B below.

The short protection circuit 800 shown in FIG. 9A operates, essentially,as an automatic switch between external charging contact 44 and batterypack 60.

Circuit 800 comprises a switch 816 that is controlled by a comparingdevice 812. In the present embodiment, switch 816 is interposed in anelectrical path between the charging contact 44 and the positiveelectrode 63 of battery pack 60. In particular, conductors 820 and 823connect one side of switch 816 to charging contact 44 and conductors 821and 824 connect the other side of switch 816 to the center electrode ofbattery pack 60.

Switch 816 in the illustrated embodiment is a p-channel MOSFET, butother electronic switching devices may also be employed. For example,other types of transistors may be employed for switch 816, includingbipolar junction transistors and other field effect transistors, such asJFETs and DE MOSFETs.

Comparing device 812 in the present embodiment comprises a voltagecomparator. However, an op amp, microprocessor, or Application SpecificIntegrated Circuit (ASIC) may also be used for comparing device 812.

One example of a power supply circuit for comparing device 812 is shownin FIG. 9B. As shown in FIG. 9B, the Vcc pin of comparing device 812, isconnected to the positive terminal of battery pack 60 and the GND pin ofcomparing device 812 is connected to ground. Although unnecessary, theVcc pin is preferably connected to the positive terminal of the batterypack 60 through a Schottky diode 830 to provide basic filtering to thesignal from the battery. A capacitor 832, of preferably 0.1 μF, isprovided in parallel with the Vcc and GND pins of the comparing device.The battery signal filtered by Schottky diode 830 may be provided viatrace 608 to the Vcc pin of microcontroller 601 to power themicrocontroller.

Comparing device 812 compares the voltage of the signal provided oninput 802 to the voltage of the signal provided on input 804. Based onthe comparison made, and the transfer characteristics of the comparingdevice, an output signal is provided on output 817 to control switch816. However, because switch 816 is a p-channel MOSFET in theillustrated embodiment, a negative gate-to-source voltage is required toenable switch 816 to conduct current.

In the present embodiment, if the voltage of the signal on input 804 isgreater than the voltage on input 802, then the comparing device 812will produce a signal with a positive voltage on output 817 that issubstantially equal to or greater than the voltage generated by batterypack 60 on conductor 824. As a result, the MOSFET comprising switch 816is disabled, and the circuit path between charging contact 44 and thecenter electrode 63 of battery pack 60 will be opened. On the otherhand, if the voltage of signal on input 802 is greater than or equal tothe voltage of the signal on input 804, then the comparing device 812will output no signal (or a 0 Volt signal) on output 817. Switch 816will be enabled to conduct current between charging contact 44 and thecenter conductor 63 of battery pack 60 under these circumstances becausethe gate-to-source voltage of the MOSFET will be negative.

In the embodiment illustrated in FIG. 9A, the voltage of signal on input802 will correspond to the voltage drop across resistor 811 providedbetween charging contact 44 and the case electrode, or ground, ofbattery pack 60. To ensure that complete charging of battery pack 60 maybe achieved, resistor 811 is preferably selected to have a resistanceslightly greater than that of resistor 810 so that a larger voltage dropoccurs across resistor 811 than resistor 810 during the chargingprocess. Preferably resistor 811 has a resistance that is greater than50% and less than or equal to about 60% of the combined total resistancefor resistors 810, 811.

The voltage of the signal provided on input 804 will correspond to thevoltage stored on capacitor 815, which in turn will depend on therespective resistances of resistors 813 and 814 in electrical path 819.In particular, because capacitor 815 is provided in parallel withresistor 814, the voltage stored on capacitor 815 will equal the voltagedrop across resistor 814. Preferably, resistors 813 and 814 are selectedto have equal values so that following equilibrium capacitor 815 willhave a charge that corresponds to approximately one half the voltage ofbattery pack 60.

By way of illustration, resistors 810, 813, and 814 may each have aresistance of 100 KΩ, and resistor 811 may have a resistance of 120 KΩ.Capacitor 815 may have a capacitance of 0.1 μF. With these values, thevoltage of the signal on input 804 will comprise approximately one halfof the voltage of battery pack 60 once capacitor 816 is charged andequilibrium is achieved in the circuit. On the other hand, the voltagedrop across resistor 811, and hence the voltage of the signal on input802, will comprise approximately 55% of the voltage drop betweencharging contact 44 and ground.

When the flashlight 10 is placed into its charging unit, externalcharging contacts 44, 48 will come into contact with correspondingcharging contacts of the charging unit so that energy may flow to thebattery pack. Based on the foregoing arrangement of short protectioncircuit 800, as long as the voltage on charging contact 44 is greaterthan or equal to the voltage of the battery pack 60, then flashlight 10is determined to be in the charging mode and switch 816 will be enabledto pass current. This is because the voltage drop across resistor 811will be greater than the voltage stored on capacitor 815 in suchcircumstances. As a result, comparing device 812, which is a voltagecomparator in the present embodiment, will signal switch 816 to close,thereby permitting energy to flow from charging contact 44 to thebattery pack 60 along lines 820, 823, 824, and 821 and the recharging ofbattery pack 60 to take place.

Further, switch 816 in the present embodiment will remain open once theflashlight is removed from the charging cradle. This is because chargingcontact 44 will be at the same potential as the center electrode 63 aslong as switch 816 is open, and, thus, the voltage of the signal oninput 802 will remain larger than the voltage of the signal on input804.

However, if the charging contacts 44 and 48 are shorted together, thevoltage between charging contact 44 and ground will quickly drop to zerovolts, as will the voltage drop across resistor 811. In response,comparing device 812 will detect that charging contact 44 is at a lowervoltage than the battery and open switch 816 by sending a signal havinga large positive voltage to switch 816 via output 817. Comparing device812 will disable switch 816 in response to a detected short more quicklythan the internal short protection circuitry 86 can detect and clear ashort. Because the internal short circuit protection circuitry 86 is nottriggered in such circumstances, battery pack 60 can continue to supplyenergy to lamp 59 without interruption by the built-in short circuitprotection circuitry 86.

In the present embodiment of short protection circuit 800, once a shortis detected between charging contacts 44 and 48, switch 816 will notopen again until the short is removed and the voltage drop betweencharging contact 44 and ground is approximately equal to or greater thanthe voltage of battery pack 60. In other words, switch 816 will not openagain until flashlight 10 is placed in its corresponding charging unit.

In addition to flashlights, short protection circuit 800 may also bebeneficially used in other rechargeable devices in which chargingcontacts are exposed. Further, while short protection circuit 800 isparticularly useful when the power source for a portable electronicdevice is a rechargeable lithium-ion battery pack, short protectioncircuit 800 may also be used advantageously in rechargeable devicespowered by other rechargeable DC power sources.

While various embodiments of an improved flashlight and its respectivecomponents have been presented in the foregoing disclosure, numerousmodifications, alterations, alternate embodiments, and alternatematerials may be contemplated by those skilled in the art and may beutilized in accomplishing the various aspects of the present invention.For example, the power control circuit and short protection circuitdescribed herein may be employed together in a flashlight or may beseparately employed. Further, the short protection circuit may be usedin rechargeable electronic devices other than flashlights. Thus, it isto be clearly understood that this description is made only by way ofexample and not as a limitation on the scope of the invention as claimedbelow.

1. A portable lighting device comprising: a main power circuit includinga power source, a light source, and an electronic power switch adaptedto regulate current flow through the main power circuit in response to avoltage; a power control circuit electrically coupled to the electronicpower switch and adapted to provide the voltage in response to a controlsignal; and a microprocessor including an output that is coupled to thepower control circuit, wherein the microprocessor provides the controlsignal to the power control circuit, and the control signal is cycledwith a sufficient duration to provide a visible flashing function to theportable lighting device, wherein the visible flashing function isperformed through the light source.
 2. A portable lighting deviceaccording to claim 1, wherein the light source has a duty cycle lessthan 17.2%.
 3. A portable lighting device according to claim 1, whereina period of the visible flashing function is approximately 1.38 seconds.4. A portable lighting device according to claim 2, wherein the dutycycle is between 1.4% and 17.2%.
 5. A portable lighting device accordingto claim 1, wherein a period of the visible flashing function is greaterthan about 1 second and less than 5 seconds.
 6. A portable lightingdevice according to claim 1, wherein said power control circuitregulates the electronic power switch when the portable lighting deviceis turned on to limit the peak current that flows through the main powercircuit prior to the main power circuit reaching a steady state.
 7. Aportable lighting device according to claim 1, wherein the power circuitmodifies the control signal to produce the voltage, and wherein thevoltage increases exponentially over time.
 8. A portable lighting deviceaccording to claim 1, wherein the light source includes a filament.
 9. Aportable lighting device according to claim 1 wherein the “on” portionof the visible flashing function is between 30 milliseconds and 250milliseconds.
 10. A portable lighting device according to claim 1further including a mechanical switch for opening and closing anelectrical path between the power source and the microprocessor, whereinthe microprocessor provides the control signal to the power controlcircuit in response to an activation signal received from the mechanicalswitch.
 11. (canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled) 15.(canceled)
 16. (canceled)
 17. (canceled)
 18. (canceled)
 19. A flashlightcomprising: a main power circuit including a power source, a lightsource, and an electronic power switch that regulates the current flowthrough the main power circuit; a microprocessor; a power controlcircuit electronically coupled to the electronic power switch andmicroprocessor, the power control circuit adapted to provide a voltageto the electronic power switch in response to a control signal from themicroprocessor; wherein the control signal has a period of greater thanabout 1 second, and wherein the power control circuit regulates currentflow through the electronic power switch in response to the controlsignal from the microprocessor to provide a visible flashing functionfor the flashlight, wherein the visible flashing function is performedthrough the light source.
 20. A flashlight according to claim 19,wherein the light source has a duty cycle of less than 17.2%. 21.(canceled)
 22. (canceled)
 23. (canceled)
 24. (canceled)
 25. (canceled)26. (canceled)
 27. (canceled)
 28. (canceled)
 29. (canceled) 30.(canceled)
 31. (canceled)
 32. (canceled)
 33. (canceled)
 34. (canceled)35. (canceled)
 36. (canceled)
 37. (canceled)
 38. (canceled) 39.(canceled)
 40. (canceled)